A Proton Irradiated CMOS On-Chip Vivaldi Antenna for 300 GHz Band Slat Array Implementation

As the CMOS transceiver reaches the sub-millimeter wave operating frequency, its circuit area cannot keep up with the shrinkage of the $0.5 \lambda_0 \times 0.5 \lambda_0$ area limit for the typical 2-dimensional (2D) tile-based phased array topology. This article proposes an end-fire on-chip Vivaldi antenna on a standard 65-nm CMOS process for the 300 GHz band operation. The Vivaldi architecture was chosen for its broadband and end-fire radiation characteristics. End-fire antenna is required for slat array topology, which enables 2 D array implementation for transceivers with circuit area above $0.5 \lambda_0 \times 0.5 \lambda_0$ . The antenna length was shortened to maximize beamwidth and reduce area. Additionally, comb-shaped slots were added to suppress side lobes and back radiation caused by the short length. To prevent higher mode surface waves from distorting the antenna radiation pattern and reducing efficiency, the substrate was thinned to $50 \mu \mathrm{m}$ . A dual-layer proton irradiation process increases the substrate resistivity to $1 \mathrm{k} \Omega$ -cm, allowing high-efficiency on-chip antenna implementation on low-cost CMOS processes. The manufactured on-chip Vivaldi antenna has an area of $0.45 \lambda_0 \times 0.45 \lambda_0$ , with measurement results showing 6 dBi gain with 1 dB flatness from 220 GHz to 320 GHz (37% bandwidth) and 76° E-plane beamwidth at 270 GHz with 87% efficiency. A $1 \times 4$ slat array implementation using the proposed on-chip Vivaldi antenna has been demonstrated, with measurement results showing a 56° beam steering range across the E-plane.